The present invention relates to a method and apparatus for changing the characteristics of a variety of devices of different scales, fields, types and so on such as plants, apparatus, microcomponents, circuits, circuit elements and so on.
Conventionally, a method of changing the characteristics of a device such as an electric circuit, an electronic circuit or the like, typically involves changing circuit constants or parameters such as resistance R, capacitance C and inductance L, changing the locations of circuit elements such as R, C, L within a circuit, or changing the entire configuration of the circuit. Such changes added to the device causes a change in the transfer function of the associated circuit, and consequently a change in an input/output response of the entire device such as time response and frequency response, and other arbitrary characteristics. Such a method provides an electric/electronic circuit having a response suitable for a particular target such as different control targets or a constant-desired-value control.
It should be noted herein that in this disclosure, the term xe2x80x9cdevicexe2x80x9d encompasses any devices which include a variety of apparatus of different scales such as plants, equipment, microcomponents, circuits, circuit elements and so on; apparatus for use in different fields such as electric, chemical, mechanical, physical fields, and apparatus of different types. Also, the xe2x80x9cdevicexe2x80x9d includes a xe2x80x9cplantxe2x80x9d or a xe2x80x9ccontrolled objectxe2x80x9d which is so called in the field of control engineering.
In respect to a change in certain characteristic of a device, the time response characteristic of a control system will be described below by way of example with reference to FIGS. 31(a) to 31(d). The graphs in FIGS. 31(a) to 31(d) are described mathematically, and are not limited to any particular target. Possible controlled objects may span in a wide range of fields including, but not limited to, a positional (angular) control for a robot arm; a voltage control for a power supply regulator; a speed control for a bullet train; and so on. For example, disturbance is called xe2x80x9cjitterxe2x80x9d in an application to frequency tracking, while disturbance is called xe2x80x9cripplexe2x80x9d in a power supply regulator. In this way, different expressions may be used for the same concept of control in different fields.
FIG. 31(a) shows that an excessively high sensitivity for a better initial response results in oscillations and high susceptibility to disturbance if a certain desired value is given for control. On the other hand, FIG. 31(b) shows that a lower sensitivity for suppressing disturbance results in a slower initial response. In this way, the sensitivity and disturbance suppression characteristics are different control targets and contradictory to each other. Conventionally, as shown in FIG. 31(c), while an attempt is made to find a control point which satisfies both of the characteristics by appropriately adjusting them, this generally results in employment of an unsatisfactory control point which is a compromise for both of the characteristics. More specifically, a control system which exhibits a relatively slow initial response and a relatively high susceptibility to disturbance is typically employed. A conventional adaptive control is intended to achieve the characteristics closest possible to those as illustrated in FIG. 31(d) by adaptively changing the sensitivity in accordance with a particular condition of a controlled object to simultaneously satisfy contradictory characteristics or control targets (the sensitivity and disturbance suppression characteristics in this example) to the utmost.
Referring now to FIGS. 32(a) and 32(b), the time responses illustrated in FIGS. 31(a)-31(d) will be described from a viewpoint of the frequency response. Whether the sensitivity (or response) is high or low can be found by examining how long a high range characteristic of a transfer function extends. More specifically, as illustrated in FIG. 32(a), a transfer function (representing the frequency characteristic of a system) exhibiting a high gain to a high frequency range may be created for increasing the sensitivity in order to improve the initial response. Conversely, as illustrated in FIG. 32(b), a transfer function exhibiting a lower gain in a high frequency range may be created for decreasing the sensitivity in order to suppress disturbance. As can be understood from the foregoing, a lower sensitivity in the high frequency range is equivalent to a reduction in gain in the high frequency range. Conventionally, many approaches falling within the foregoing category have been proposed to adjust the high frequency range characteristic without damaging the low frequency characteristic.
A specific example of a device required to address contradictory characteristics may be a phase locked loop (PLL) circuit. The PLL typically comprises a controller for controlling a voltage controlled oscillator (VCO), so that circuit constants, circuit configuration and so on of the controller are manipulated to design the PLL to have desirable follow-up speed, stability and so on of oscillating frequencies. Among a wide variety of PLLs, a xe2x80x9ctime optimal PLLxe2x80x9d is known as an example which pursues the response speed rather than jitter suppression. The time optimal PLL has been published, for example, in an article entitled xe2x80x9cTime optimal PLL Using High Speed Null Methodxe2x80x9d by Kobayashi et al, Transactions of Sensing Instrument Control Engineering Systems Information Computer Ergonomics (SICE), 16-4, pp573-578, 1980.
While the foregoing description has been directed particularly to a typical problem in the prior art on a control system including a PLL, similar problems are encountered also in devices such as apparatus of any fields, scales, types and so on which require adjustments of contradictory characteristics, not limited in electric/electronic circuits. For example, similar problems may be encountered in large-scaled plants, electronic apparatus such as computers, electronic devices such as microcomponents, sensors or the like, semiconductor circuits, and so on.
Also, other examples of contradictory characteristics, which require appropriate adjustments, may be resolution and drawing speed, resolution and conversion speed of an A/D converter, and a variety of other paired characteristics, in addition to the aforementioned response speed and disturbance suppression characteristics.
Since the above-mentioned prior art changes the characteristic of a device only using existing design parameters such as circuit constants, circuit configuration, and so on of the xe2x80x9cdevice,xe2x80x9d complicated design procedures are often required for further improving the characteristics of the overall device. In addition, the realization of contradictory characteristics inevitably involves a considerable compromise, so that it is quite difficult to actually realize contradictory characteristics simultaneously.
It is therefore an object of the present invention to provide a method and apparatus for changing the characteristics of devices such as a variety of plants, equipment, circuits, semiconductor devices, and so on in a variety of fields, a variety of scales, a variety of applications, a variety of types, and so on, in a manner different from the prior art.
It is another object of the present invention to provide a method and apparatus for controlling a controlled object in a manner different from the prior art.
It is a further object of the present invention to provide a control method and apparatus which are capable of simultaneously realizing contradictory characteristics such as operation, performance and so on in the prior art.
It is a further object of the present invention to provide a method and apparatus which are capable of improving the characteristics of a device such as the operation and performance more than the prior art.
To achieve the above objects, the present invention employs the concept of time scale in changing the characteristics of a device.
Specifically, a device characteristic changing method according to the present invention changes a characteristic of the device by changing a time scale on which the device operates.
Also, a device characteristic changing apparatus for changing a characteristic of a device according to the present invention comprises time scale generating means for generating a time scale on which a device operates, and time scale changing means for changing the time scale, wherein a characteristic of the device is changed by changing the time scale on which the device operates.
According to the present invention, the device may have a first characteristic when it operates on a first time scale, and have a second characteristic when it operate on a second time scale different from the first time scale.
Also, according to the present invention, the characteristic may be a time dependent characteristic. In this case, the time dependent characteristic may be an input/output response characteristic of the device.
Also, in this case, the input/output response may be an input/output response which depends on the frequency of the device.
Further, according to the present invention, the characteristic may be changed to achieve different control targets, or to achieve a predetermined desired value. Also, the characteristic may be changed while maintaining a transfer function of the device substantially constant, or the changing of the characteristic is accompanied by changing of a transfer function of said device. Furthermore, the changing of the characteristic is accompanied or is not accompanied by changing of an element which affects a characteristic of the device other than the time scale.
Also, according to the present invention, the device may be a device which operates on different time scales to have substantially different characteristics from each other, and is operable on a variable time scale. The device may also include a device in an electric, mechanic, chemical or physical field. Further, the device may include a plant, equipment, a microcomponent, a circuit, or a circuit element. The device may operate in a digital form or in an analog form. The device may be a controller for use in a control system for controlling a controlled object. In this case, the control device may perform a feedforward control or perform a feedback control.
Further, according to the present invention, the time scale of the device may be determined in response to a signal external to the device or in response to a signal internal to the device. The transfer function of the device may be maintained substantially constant irrespective of a change in the time scale. The time scale may include real time as a time scale. A change in the time scale may include a change to an arbitrary number of time scales. The time scale may be changed in accordance with a predetermined sequence of time scales. In this case, the predetermined sequence may be determined for an adaptive control for achieving different control targets.
According to the present invention, a method of operating a device is also provided, wherein the method includes the device characteristic changing method.
Furthermore, according to the present invention, a device system including the aforementioned device characteristic changing apparatus, and a device is also provided.
Also, according to the present invention, a method of controlling a controlled object in response to an input signal includes the steps of generating a manipulated variable for the controlled object in response to the input signal in accordance with a predetermined transfer function including a time constant, generating a state value representative of a state of the controlled object, generating a time scale changing value from the state value using a predetermined time scale changing function, and changing the time constant of the transfer function in response to the time scale changing value.
According to the present invention, the control method may further include the step of providing the transfer function by transfer element means included in a controller which is used in a control system for controlling the controlled object. The control method may further include the step of generating a time scale on which the transfer element means operates. Also, the step of generating a state value may include generating the state value of the controlled object by observing a state within the control system.
Also, according to the present invention, a controller for use in a control system for controlling a controlled object in response to an input signal, comprises time scale generating means for generating a predetermined time scale, transfer element means having a predetermined transfer function for operating on the predetermined time scale, observing means for observing a state within the control system to generate a state value indicative of a state of the controlled object, time scale changing means having a predetermined time scale changing function, and for generating a time scale changing value derived from the predetermined time scale changing function with the state value from the observing means used as an input, and time scale changing means for changing the predetermined time scale in response to the time scale changing value.
Also, according to the present invention, in the control method and the controller, a change in the transfer function resulting from a change in the time constant may be compensated.
The generation of a time scale changing value may be performed by generating a first evaluation value from the state value using a first evaluation function, generating a second evaluation value from the state value using a second evaluation function, setting a predetermined first threshold value, setting a predetermined second threshold value, comparing the first evaluation value with the first threshold value to set the time scale changing value to an initial value when the first evaluation value is higher than the first threshold value, and comparing the second evaluation value with the second threshold value to update the time scale changing value when the second evaluation value is lower than the second threshold value.
Also, according to the present invention, the first and second threshold values may be equal, and the first and second evaluation functions may be equal. The initial value may be one, and the time scale changing value may be updated increasingly. Alternatively, the initial value may be a predetermined value, and the time scale changing value is updated increasingly or decreasingly.
The time scale changing value is updated by increasing the value in a predetermined sequence. The predetermined sequence may be an additive or multiplicative sequence.
Further, according to the present invention, a change in the time constant may include scaling up or scaling down the time scale in response to the time scale changing value. The scaling-up/scaling-down of the time scale may include using a reference signal generating means for generating a reference signal at a variable frequency. The reference signal generating means may generate the reference signal at a variable frequency by dropping an oscillating pulse and inserting the oscillating pulse.
Also, according to the present invention, the input signal may be a signal indicative of a desired value inputted to the control system, a signal indicative of a difference between a desired value inputted to the control system and a feedback value in the control system.
Also, according to the present invention, the transfer element means may include at least one of a derivative element, an integral element, a first-order lag element, a second-order lag element, and a dead time element.
Also, according to the present invention, the controller may comprise a discrete value system. Alternatively, the controller may comprise a continuous value system. In this case, the controller may include sampling means for sampling the input signal to generate a sampled input signal.
Further, according to the present invention, the control system may be a PLL circuit, or a time optimal PLL circuit.
Also, according to the present invention, a method of operating a controlled object is provided, wherein the method includes the aforementioned control method.
Further, according to the present invention, a control system including the aforementioned controller, and a controlled object is also provided.
The above and other objects, features, advantages of the present invention will become more apparent from the following description of the preferred embodiments, when taken in conjunction of the accompanying drawings.